Genetic and hereditary influences that give rise to variation in the magnitude and direction of lateralization are presently the least understood processes in the etiology of lateralization of function and cerebral specialization. Because mice exhibit marked asymmetries of behavior that are analogous, if not prototypic, to the expressed functional asymmetries of human beings, and because the knowledge of the mouse is far more advanced than that of any other mammal, studies of the hereditary bases of laterality in mice can make unique contributions to an understanding of the etiology of lateralization of function and cerebral dominance. The objective of this proposed research is to gain an understanding of the genetic, hereditary, behavioral, and developmental processes leading to variability in the expression of lateral specialization in genetically defined and definable strains and stocks of mice. The long-term goal is to create and characterize practical experimental models of variable lateralization that may prove useful for the study of the specific behavioral differences, deficits, and associated psychopathology that may be associated with the variability of lateralization in humans. Mice of standardized inbred strains will be the primary subjects of this research. Special emphasis will be placed on behavior genetic studies of the processes that maintain differences in the degree of strength of lateralization, of the complex genetic-environment interactions that lead to expression of the directed senses of asymmetries, and of the organization of pairs of asymmetries in mice possessing congenital unilateral defects of sensory function. Theoretical studies will be conducted to discover the patterns of the inheritance of asymmetry vectors that will be important to understanding the results of animal as well as human studies.